JP2003302709A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader which suppresses not only performance lowering due to temperature change but also manufacturing cost increase therefrom. <P>SOLUTION: A lens 38 and a linear image sensor 42 in which change of relative positional relation greatly affects reading-out performance are fixed to a first member 34 which is constituted of a molding such as an aluminum die cast and has very small coefficient of linear expansion. A mirror 70 in which change of relative positional relation less affects the reading-out performance is fixed to a second member 32 which is constituted of a plastic molding made of PPE, PE or the like having coefficient of linear expansion being rather small but larger than that of the first member 34. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly to the structure of its carriage.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus including a linear image sensor such as an image scanner or a copying machine is provided with a mechanism for moving a scanning line on a document in a direction perpendicular to the scanning line. In an image reading apparatus having a flat platen, a scanning line is moved by moving a carriage that carries an optical system such as a mirror and a lens and a linear image sensor in parallel with a platen surface of the platen.

When the carriage is deformed due to a temperature change, the relative positional relationship among the document, the light source, the mirror, the lens, and the linear image sensor is changed, so that the reading performance using the resolution, the accuracy of the reading range, and the like as indicators is significantly deteriorated. . In order to prevent performance deterioration due to temperature changes, it is desirable for the carriage to have high dimensional stability with a linear expansion coefficient as an index. Further, in order to reduce the load on a drive system such as a motor that moves the carriage, it is desirable that the carriage be lightweight. Generally, high-end model carriages are made of metal moldings such as aluminum die castings, and low-priced carriages are made of plastic moldings made of polyphenylene ether (PPE), polycarbonate (PC), etc. .

[0004]

However, although the metallic molded article has high dimensional stability, it is heavier and more expensive than the plastic molded article. On the other hand, plastic molded products are lighter and cheaper than metallic molded products, but have lower dimensional stability than metallic molded products. In addition, molded products of plastics such as polyphenylene sulfide (PPS) having high dimensional stability and molded products of composite materials in which a reinforcing material such as glass fiber is mixed in a plastic base material have high dimensional stability and are lightweight, but the manufacturing cost is high. Is difficult to reduce.

The present invention has been made in view of the above problems, and an object thereof is to provide an image reading apparatus which suppresses performance deterioration due to temperature change and suppresses increase in manufacturing cost. And

[0006]

An image reading apparatus according to a first aspect of the present invention comprises a linear image sensor and a reduction optical system for reducing an image of a document placed on a document table on the linear image sensor to form an image. An image reading apparatus comprising a carriage for carrying the platen of the document table in parallel, wherein the carriage includes a first member holding the linear image sensor and a lens of the reduction optical system, and the reduction optical system. The first member includes a second member holding a mirror forming an optical path from the original to the lens, and a coupling means for integrally coupling the first member and the second member together. The linear expansion coefficient of is smaller than the linear expansion coefficient of the second member. In this specification, the term "base material" is used to include not only the base material that is the base of the composite material but also the non-composite material. In the reduction optical system of the image reading apparatus, the change in the positional relationship between the lens and the linear image sensor has a greater effect on the reading performance than the change in the positional relationship between the lens, the mirror, and the document surface. Therefore, the part that holds the lens and the linear image sensor and the part that holds the mirror are formed by separate members, and the first member having a relatively small coefficient of linear expansion is used for the part that holds the lens and the linear image sensor. By using the second member having a relatively large coefficient of linear expansion for the portion holding the mirror, it is possible to suppress performance deterioration due to temperature change and suppress increase in manufacturing cost due to the performance deterioration.

In the image reading device according to the second aspect,
The base material of the first member is metal, and the base material of the second member is plastic. As a result, it is possible to reduce the weight of the carriage as compared with the case where the entire carriage is made of a metallic molded product while suppressing the performance deterioration due to the temperature change.

According to another aspect of the image reading device of the present invention,
The base material of the first member and the base material of the second member are both plastic. By making both the base material of the first member and the base material of the second member plastic, the weight of the carriage can be further reduced.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below based on an embodiment. FIG. 2 is a block diagram showing an image scanner according to an embodiment of the present invention.

The light source 10 is composed of a tube lighting device such as a fluorescent tube lamp. The light source 10 irradiates the vicinity of the scanning line of the document 16. The reduction optical system 50 is composed of a mirror and a lens described later. The reduction optical system 50 reduces a reflected light image or a transmitted light image on the scanning line of the document 16 with which the light source 10 is irradiated on the linear image sensor 42 to form an image.

The linear image sensor 42 scans the optical image on the scanning line formed by the reduction optical system 50, and outputs an electric signal that correlates with the density of the optical image. The linear image sensor 42 accumulates electric charges obtained by photoelectrically converting light in a predetermined wavelength region such as visible light, infrared light, and ultraviolet light in a light receiving element such as a photodiode for a certain period of time, and receives light amount of each light receiving element. The electrical signal corresponding to the CCD (Charge Coupled D
evice), and output using a MOS transistor switch.

The main scanning drive section 68 is a drive circuit for outputting to the linear image sensor 42 drive pulses necessary for driving the linear image sensor 42. The main scanning drive unit 68 includes, for example, a synchronization signal generator, a drive timing generator, and the like.

The sub-scanning drive unit 66 is composed of a belt locked to a carriage described later, a motor and a gear train for rotating the belt, a drive circuit, and the like. When the sub-scanning drive unit 66 pulls the carriage by the belt, the scanning line moves in the direction (sub-scanning direction) perpendicular to the belt, so that the two-dimensional image can be scanned.

The AFE (Analog Front End) section 52 is composed of an analog signal processing section, an A / D converter and the like. The analog signal processing unit performs analog signal processing such as amplification and noise reduction processing on the electric signal output from the linear image sensor 42, and outputs the electric signal. The A / D converter quantizes the electric signal output from the analog signal processing unit into an output signal in digital representation having a predetermined bit length and outputs the output signal.

The digital image processing section 54 includes an AFE section 5
Image data is created by performing processing such as gamma correction, defective pixel interpolation by a pixel interpolation method, shading correction, and sharpening of the image signal on the output signal output from No. 2.
The above-mentioned various processes performed by the digital image processing unit 54 may be replaced with processes by a computer program executed by the control unit 56. Digital image processing unit 54
The image data created in step 1 is transferred to a personal computer (PC) or the like via an interface (not shown).

The control unit 56 includes a CPU 58, a ROM 60 and a RAM 62. The CPU 58 executes a computer program stored in the ROM 60 and controls each unit of the image scanner. The ROM 60 is a memory that stores computer programs executed by the CPU 58 and various data, and the RAM 62 is a memory that temporarily stores programs and various data.

FIG. 1 is a schematic sectional view showing the structure of an image scanner according to an embodiment of the present invention. Platen 20
Is formed of a transparent plate such as a generally rectangular glass plate, and an original 16 such as a photographic film, a photograph, or a printed document is placed on the plate surface 18 thereof. The document table 20 is fixed to a case (not shown).

The carriage 36 includes the light source 10 and the mirror 7.
A second member 32 that accommodates and holds 0 and a first member 34 that accommodates and holds the lens 38 and the linear image sensor 42 are provided. The carriage 36 is pulled by a belt (not shown) of the sub-scanning drive unit 66 and guided by the shaft 22 to move in parallel with the plate surface 18 of the document table 20, and moves the light source 10, the mirror 70, the lens 38, and the linear image sensor 42 to the document table. It is carried parallel to the board surface 18 of 20.

The second member 32 is slidably fitted to the shaft 22 fixed to the case in a posture parallel to the plate surface 18 of the document table 20. The second member 32 is PPE, PC
It is composed of an inexpensive injection-molded plastic product having a small linear expansion coefficient. The linear expansion coefficient of PPE is 3-4 (1
0 ^-5 / K), the linear expansion coefficient of PC is 3-5 (10 ^-5 / K)
Is. As the base material of the second member 32, PPE or PE
The material is not limited to the above, and any material may be used as long as it has a linear expansion coefficient similar to those of the above materials. The second member 32 is formed as a dark box in which at least two openings are formed by joining two or more plastic molded products together. The first opening 14 is for guiding the reflected light of the document 16 into the carriage 36. The second opening 30 is for guiding the light reflected by the mirror 70 to the lens 38.

The light source 10 is fixed to the second member 32 in the vicinity of the document table 20 with the longitudinal axis thereof extending parallel to the longitudinal axis of the linear image sensor 42.
The light source 10 may be provided above the document table 20 to read a transparent document.

The mirror 70 is composed of a first mirror 28, a second mirror 24, a third mirror 48 and a fourth mirror 26, each of which has an elongated rectangular reflecting surface. The first mirror 28, the second mirror 24, the third mirror 48, and the fourth mirror 26 have their longitudinal axes in the plate surface 18 of the document table 20.
It is fixed to the second member 32 in a posture in which the optical path extending from the original 16 to the lens 38 is formed in parallel with.

The first member 34 is integrally connected to the second member 32 by a screw 46 as a connecting means described in the claims.
The means for connecting the second member 32 and the first member 34 may be, for example, adhesive bonding or fitting using elastic deformation, in addition to screws. The first member 34 has two openings, one opening is closed by the substrate 44, and the other opening is configured as a dark box continuous with the second opening 30 of the second member 32.

The first member 34 is composed of a die-cast product made of metal such as aluminum or an injection-molded product made of plastic such as PPS having a linear expansion coefficient smaller than that of the first member. The coefficient of linear expansion of aluminum die casting is about 2 (10 ^-5 /
K), the coefficient of linear expansion of PPS is 0.6 to 2 (10 ^-5 / K)
Is. The base material of the first member 34 is aluminum or PP.
The material is not limited to S, and any material may be used as long as it has a linear expansion coefficient similar to that of S.
Further, the base material of the second member 32 and the base material of the first member 34 are made the same, and the linear expansion coefficient of the first member 34 is made smaller than that of the second member 32 by changing the ratio of the respective reinforcing materials. Good.

The lens 38 is composed of a single lens or a compound lens in which the optical axes thereof are matched and combined. The lens 38 is held by a lens barrel 40. The lens barrel 40 is fixed to the inside of the first member 34 by screws, adhesion, or the like.

The substrate 44 is fixed to the first member 34 by a screw or the like (not shown) at a position where one opening of the first member 34 is closed. The linear image sensor 42 is surface-mounted on the substrate 44 such that the light receiving elements are arranged in parallel with the plate surface 18 of the document table 20 on a plane perpendicular to the longitudinal axis of the shaft 22. Further, the main scanning drive unit 68 and A are provided on the substrate 44.
Various electronic components forming the FE unit 52 are mounted.

FIG. 3 is an optical path development view of a reduction optical system according to an embodiment of the present invention. The reflected light or transmitted light of the original 16 is reflected by the mirror 70, refracted by the lens 38, and enters the light receiving element of the linear image sensor 42, whereby the optical image on the scanning line of the original 16 is reduced and the linear image sensor 42 is reduced. Is imaged.

Next, in the optical path from the original 16 to the linear image sensor 42, the first section from the lens 38 to the linear image sensor 42 and the original 16 to the lens 38.
The influence of the change in the relative positional relationship of the optical elements in the second section up to the above on the optical image input to the linear image sensor 42 will be described. In order to obtain the resolution of the lens 38, the light receiving element of the linear image sensor 42 must be positioned within the depth of focus of the lens 38. Since this depth of focus is extremely smaller than the optical path length of the first section, the resolution of the lens 38 is likely to decrease if the relative positional relationship between the lens 38 and the linear image sensor 42 changes. Further, in the reduction optical system, the change in the optical path length from the lens 38 to the focus position due to the change in the optical path length from the lens 38 to the original 16 is smaller than the change in the optical path length from the lens 38 to the original 16. In other words, the lens 38
If the optical path length from the linear image sensor 42 to the linear image sensor 42 changes, the position of the document 16 where a clear image can be input to the linear image sensor 42 moves by a larger amount than the amount of change. In short, in the second section, inside the mirror 70 or the mirror 70
When the relative positional relationship between the lens 38 and the linear image sensor 42 changes in the first section as compared with the relative positional relationship between the lens 38 and the lens 38, the change in the positional relationship is the resolution and the reading range. Has a great influence on the reading performance using the accuracy of the index as an index. Therefore, as compared with the case where the entire carriage is formed of an inexpensive plastic molded product such as PPE or PE, the effect of suppressing the performance deterioration due to the temperature change by forming the first member 34 by aluminum die casting or the like is considerably large.

In the reduction optical system 50, the optical path of the first section is considerably short and narrow with respect to the optical path from the original 16 to the linear image sensor 42. That is, the physique of the first member 34 can be made considerably smaller than the physique of the entire carriage 36. Therefore, by constructing the first member 34 with a generally expensive molded product such as aluminum die-casting, the manufacturing cost and weight are considerably increased as compared with the case where the entire carriage is constructed with an inexpensive plastic molded product such as PPE or PE. small.

According to the image scanner of this embodiment, the lens 38 and the linear image sensor 42 arranged in the first section are fixed to the first member 34 which is formed of a molded product such as aluminum die cast and has a very small linear expansion coefficient. However, since the mirror 70 arranged in the second section is fixed to the second member 32 which is made of a plastic molded product and has a coefficient of expansion such as PPE, PE, etc. which is relatively small, but is larger than the first member 34, it is affected by temperature change. It is possible to suppress the deterioration of the performance and suppress the increase of the manufacturing cost and the weight of the carriage due to the deterioration of the performance.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an image scanner according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an image scanner according to an embodiment of the present invention.

FIG. 3 is a development view of optical paths of an optical system according to an embodiment of the present invention.

[Explanation of symbols]

10 light sources 16 manuscripts 18 board 20 Platen 32 Second member 34 First member 36 carriage 38 lenses 42 Linear image sensor 46 screw (coupling means) 50 reduction optical system 70 mirror

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H108 AA02 CB01 HA01 JA00                 2H109 DA31                 5C072 AA01 BA12 CA04 DA02 DA04                       DA21 EA05 LA02 XA01

Claims (3)

[Claims] 1. An image reading device including a linear image sensor and a carriage for carrying a document placed on a document table in parallel with a plate surface of the document table, and a reduction optical system for reducing and forming an image on the document image on the linear image sensor. In the apparatus, the carriage includes a first member that holds the linear image sensor and a lens of the reduction optical system, and a mirror that forms an optical path from the document of the reduction optical system to the lens. It has a holding second member, a coupling means for integrally coupling the first member and the second member, the linear expansion coefficient of the first member is from the linear expansion coefficient of the second member. An image reading device characterized by being small. 2. The image reading apparatus according to claim 1, wherein the base material of the first member is metal, and the base material of the second member is plastic. 3. The image reading apparatus according to claim 1, wherein the base material of the first member and the base material of the second member are both plastic.